Incorporate ideas from the C++ numerics library

[wolfram77]

Take a look at the following improvements. Include any additional functions that were not previously mentioned.

Error and gamma functions

• erf
• erfc
• tgamma
• lgamma

Mathematical special functions

• assoc_laguerre*
• assoc_legendre*
• beta*
• comp_ellint_1*
• comp_ellint_2*
• comp_ellint_3*
• cyl_bessel_i*
• cyl_bessel_j*
• cyl_bessel_k*
• cyl_neumann*
• ellint_1*
• ellint_2*
• ellint_3*
• expint*
• hermite*
• legendre*
• laguerre*
• riemann_zeta*
• sph_bessel*
• sph_legendre*
• sph_neumann*